Image source is the link to the image itself that has an extension of .jpg/.png/.gif
Images from Facebook will most likely will not work.
On that note do not paste links from the address bar since it'll most likely be a website which of course isn't an image.

How do I get this image link? Modern browsers nowadays can get the link of the image by Right-Clicking on the image and choose Copy Image Address.

To test this paste this into the address and if it only shows an image then it's good post.

If after post into the forum and it appears broke, PLEASE use the Edit button to edit the post RATHER than posting a new post.